Thermoplastic parts are being used to replace metal in different applications where their weight and cost are lower than various metals that could be used. Plastic parts that are molded or thermoformed can be coated after being formed with various types of coatings, but typically these coatings will not adhere well to the plastic substrate and eventually flake off or are easily abraded off. There is also some difficulty obtaining uniform coverage on odd shapes.
Clear or colored, decorative or protective discrete coatings are cast from solvent-based coatings onto the surface of objects made of thermoplastic materials. Such coatings have conventionally been introduced by applying solvent-based paints or coating compositions onto the surface of preformed thermoplastic objects. The coating layers are discrete coatings which means the paint, after solvent volatilization, creates a coating that rests upon the surface of the thermoplastic substrate without intimate bonding between the polymers of the substrate and the coating composition. Such paints have been used to form coatings on a variety of materials made in a variety of thermoplastic processes such as injection molding, thermoforming, blow molding, etc.
In conventional thermoforming processes, sheet thermoplastic material is cut to a predetermined size, introduced into a thermoforming machine, is heated and formed into a desired shape or geometry. Once the thermoformed article is shaped, coatings have commonly been applied through spray-on, brush-on, curtain coating, or other application technology. Such conventional technology using typical solvent-based paint formulations form discrete coatings on the surface of the thermoformed objects. Such paint formulations contain in a solvent base common polymeric bonding agents, pigments and other common paint ingredients. The formation of such coatings is desirable in order to provide an attractive colored appearance, informational legends, or protection from scratches or other mechanical insult. Such coatings are not intimately bonded or integral with the underlying thermoplastic matrix. Such solvent-based paints have been used for many years. However, the discrete coatings obtained from these paints commonly are not sufficiently resistant to chip, scratch or other coating removal mechanisms such as weathering. Such discrete coatings are easily removed in day-to-day use through relatively minor mechanical impact from day-to-day wear and tear.